The present invention relates to a method and apparatus for delivering an aerosol, nebulized liquid or solid medicine or a vapor to a patient's respiratory tract, and more particularly, the present invention relates to an improved nebulizer that provides an aerosol more efficiently and with improved particle size uniformity.
Medical nebulizers for generating a fine spray or nebula of a liquid medicine that can be inhaled by a patient are well known devices commonly used for the treatment of certain conditions and diseases. Nebulizers have applications in treatments for conscious, spontaneously-breathing patients and for controlled ventilated patients.
In some nebulizers, a gas and a liquid are mixed together and directed against a baffle. As a result, the liquid is aerosolized, that is, the liquid is caused to form into small particles that are suspended in the air. This aerosol of the liquid can then be inhaled into a patient's respiratory tract. One way to mix the gas and liquid together in a nebulizer is to pass a quickly moving gas over a liquid orifice tip of a tube. The negative pressure created by the flow of pressurized gas is a factor that contributes to drawing the liquid out of the liquid orifice tip into the stream of gas and nebulize it.
Some of the considerations in the design and operation of nebulizers include regulation of dosages and maintenance of consistent aerosol particle size. In conventional nebulizer design, pressurized gas may entrain a liquid against a baffle on a continuous basis until the liquid in a reservoir is depleted. Continuous nebulization may result in a waste of aerosol during a patient's exhalation or during a delay between a patient's inhalation and exhalation. This effect may also complicate regulation of dosages because the amount of wasted aerosol may be difficult to quantify. Also, continuous nebulization may affect particle size and/or density. In addition, there may be excess medication lost to condensation on the nebulizer or mouthpiece during periods of non-inhalation. On the other hand, interrupted nebulization may also affect particle size and density as the nebulization is turned on and off.
There are several other considerations that relate to the effectiveness of nebulizer therapies. For example, it has been suggested that nebulization therapy is more effective when the generation of aerosol particles is relatively uniform, for example, producing particles of a particular size, particles within a range of sizes, and/or particles a substantial percentage of which are within a range of sizes. One particle size range that has been considered to be appropriate for inhalation therapy includes a particle size range of approximately 0.5 to 2 microns. Other particle size ranges may be suitable or preferable for particular applications. Generally, large and small size droplets should be minimized. It has also been considered desirable for some inhalation therapies that a substantial percentage, e.g. over 75%, of the aerosol particles be less than approximately 5 microns depending on the desired area of particle deposition in the respiratory tract. In addition, it may be advantageous for a nebulizer to be able to generate a large amount of aerosol quickly and uniformly so that a proper dosage can be administered.
Accordingly, with these considerations taken into account, there is a need for an improved nebulizer.